for pratice i was going to use a 10gb, to make sure everything was good to go.

The smallest Hard drive TiVo ever used I think was a 15Gb on the original Series 1, your drive would have to be i would guess at least 40Gb, and even that may not work if the sector count is less than the TiVo 40Gb drive. A Humax DVD TiVo had fewer sectors than the TiVo 540 on the 40Gb drive.

the 1 that died is a maxtor quickview 40gb and the spare i have is a maxtor 80gb. Another question, i have software that i use for coping hard drives for my computers when i upgrade them, any chance i can copy my tivo drive ?

the 1 that died is a maxtor quickview 40gb and the spare i have is a maxtor 80gb. Another question, i have software that i use for coping hard drives for my computers when i upgrade them, any chance i can copy my tivo drive ?

You can't use those programs, but there is something similar designed specifically for tivo: